In recent years, thermal transfer systems have been developed to obtain prints from pictures that have been generated electronically from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to one of the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271.
Exposure of dyes to ultraviolet light (light with wavelengths less than 400 nm) usually results in degradation, or fading, of dyes with time. The degradation can be caused by photolysis, which is the direct absorption of the ultraviolet light. The dye can also degrade by either photooxidation or photoreduction depending on the chemical structure of the dye and of the natural or man-made polymer surrounding the dye. It is common to include a UV absorbing material in a heat-transferable protective overcoat layer for a dye-diffusion thermal transfer print as taught in U.S. No. Pat. 4,522,881 to reduce the rate of dye fading from ultraviolet light. Protection of the printed image from UV light should not degrade the stability of the image to daylight, which has a much lower intensity of UV light. Normally, some of the UV absorbing material diffuses into the receiving layer during transfer of the over protective layer. The material can then interact with either the dyes in the receiver layer or the polymers that make up the receiving layer. A negative interaction can cause the dyes to fade more rapidly in the presence of small amounts of the UV absorbing agent than in its absence when exposed to either daylight or sunlight.
U.S. Pat. No. 6,184,375 suggests the use of triazine UV absorbers for a broad range of uses. It is suggested to employ such materials in various locations such as the receiver layer or in the overcoat as described in EP 505,734.
It is a problem to be solved to provide a thermal dye transfer imaging element containing a UV absorber that provides the image improved resistance to degradation from UV light exposure without degrading the resistance of the image to daylight exposure.